If she got sick from the swim, she got unlucky because the bacteria levels were "very good". She probably got sick from somewhere else.

It was not E. coli that made her sick, she wrote, adding that she sought treatment at a clinic in the Olympic Village on Sunday after several days of vomiting and diarrhea “left me quite empty.”

World Triathlon said the bacteria levels last week when the individual triathlon events were held were considered “very good” and that the levels were also within acceptable limits during Monday’s triathlon mixed relay event.

source: https://apnews.com/article/olympics-2024-paris-seine-water-quality-triathlon-6a5bbed0ab542a45314ebb21a2ac1840